Trypanosomes can initiate nuclear export co-transcriptionally
ABSTRACT: The nuclear envelope serves as important mRNA surveillance system. In yeast and human, several control systems act in parallel to prevent nuclear export of unprocessed mRNAs. Trypanosomes lack homologues to most of the involved proteins and their nuclear mRNA metabolism is non-conventional exemplified by polycistronic transcription and mRNA processing by trans-splicing. We here visualised nuclear export in trypanosomes by probing large, endogenous mRNA by intramolecular multi-colour single molecule FISH (smFISH). In addition, unspliced mRNAs were visualised by co-probing two adjacent introns or intergenic regions. We found that the initation of nuclear export requires neither the completion of transcription nor trans-splicing. Nevertheless, the inhibition of trans-splicing blocked cytoplasmic transport of the of unspliced mRNAs and only a small fraction reached the nucleus-distant cytoplasm. Most of the unspliced transcripts remained at the nuclear periphery, within transport and in nuclear periphery granules (NPGs) localised at the cytoplasmic site of nuclear pores that resemble stress granules in composition. Our work shows that, in striking contrast to other eukaryotes, trypanosomes can start nuclear export while the mRNA is still transcribed, but unspliced transcripts remain ‘stuck’ in nuclear pores, probably awaiting processing or decay. Our data indicate that trypanosomes regulate the completion of nuclear export rather than the start.
Project description:Eukaryotic cells have to prevent the export of unspliced pre-mRNAs until intron removal is completed to avoid the expression of aberrant and potentially harmful proteins. Only mature RNAs associate with the export receptor Mex67 (mammalian TAP) and enter the cytoplasm. The underlying nuclear quality control mechanisms are still unclear. Here we show that two shuttling SR-proteins Gbp2 and Hrb1 are key surveillance factors for the selective export of spliced mRNAs in yeast. Their absence leads to the significant leakage of unspliced pre-mRNAs into the cytoplasm. They bind to pre-mRNAs and the spliceosome during splicing, where they are necessary for the surveillance of splicing and the stable binding of the TRAMP-complex to the spliceosome-bound transcripts. Faulty transcripts are marked for their degradation at the nuclear exosome. On correct mRNAs the SR-proteins recruit Mex67 upon completion of splicing to allow a quality controlled nuclear export. Altogether, these data identify a role for shuttling SR-proteins in mRNA surveillance and nuclear mRNA quality control. 6 samples, i.e. 2 replicates per protein Gbp2, Hrb1 and Npl3
Project description:Trypanosome RNA polymerase II transcription is polycistronic, individual mRNAs being excised by trans splicing and polyadenylation. In this study, we refined the previously published mathematical model for bloodstream form parasites and extended it to the procyclic form. We used the model, together with known mRNA half-lives, to predict the abundances of individual mRNAs, assuming rapid, unregulated mRNA processing; then we compared the results with measured mRNA abundances. Remarkably, the abundances of most mRNAs in procyclic forms are predicted quite well by the model, being largely explained by variations in mRNA decay rates and length. In bloodstream forms substantially more mRNAs are less abundant than predicted. We list mRNAs that are likely to show particularly slow or inefficient processing, either in both forms or with developmental regulation. We also measured ribosome occupancies of all mRNAs in trypanosomes grown in the same conditions as were used to measure mRNA turnover. In procyclic forms there was a weak positive correlation between ribosome density and mRNA half-life, suggesting cross-talk between translation and mRNA decay; ribosome density was related to the proportion of the mRNA on polysomes, indicating control of translation initiation. Ribosomal protein mRNAs in procyclics appeared to be exceptionally rapidly processed but poorly translated. Through this study, we conclude that lLevels of mRNAs in procyclic form trypanosomes are determined mainly by length and mRNA decay, with some control of precursor processing. In bloodstream forms variations in nuclear events play a larger role in transcriptome regulation, suggesting acquisition of new control mechanisms during adaptation to mammalian parasitism. Ribosome profiling and mRNA libraries were constructed in triplicate from in vitro PCF and in duplicate from in vitro T. brucei Lister427, to understand global differntial gene transcription.
Project description:Three shuttling SR-like proteins exist in Saccharomyces cerevisiae, Npl3, Gbp2 and Hrb1, that are involved in the nuclear export of mRNAs. In a screen for genes that regulate the export of Gbp2, we identified novel mutants of the splicing factors PRP8 and PRP17 that lead to severe mislocalization defects for Gbp2 and Hrb1, but not Npl3. Microarray and qRT-PCR analyses show that Gbp2 and Hrb1 preferentially bind to transcripts derived from intron-containing genes. Moreover, in contrast to Npl3, Gbp2 and Hrb1 show genetic and physical interactions with late splicing factors such as Prp17 and Prp43. Further, RNA co-immunoprecipitation experiments reveal that, unlike Npl3, association of Gbp2 and Hrb1 with the mRNA requires splicing, and this in turn is required for their Mex67 recruitment. We propose a model in which Gbp2 and Hrb1 are attached to the mRNAs at late stages of splicing to promote the subsequent export of spliced mRNAs. keyword: RIP-chip RNA-IP of endogenously expressed 3-fold C-terminal myc-tagged Gbp2 and Hrb1 in S288C background cells was each performed once in cells grown to a density of 4x10^7 cells/ml and hybridized against a total (input) RNA reference.
Project description:The nuclear phase of the gene expression pathway culminates in the export of mature mRNAs to the cytoplasm through nuclear pore complexes (NPCs). GANP (Germinal-centre Associated Nuclear Protein) promotes the transfer to NPCs of mRNAs bound to the transport factor NXF1. Here, we demonstrate that GANP, subunit of the TREX-2 mRNA export complex, promotes selective nuclear export of a specific subset of mRNAs whose transport depends on NXF1. Genome-wide gene expression profiling showed that half of the transcripts whose nuclear export was impaired following NXF1 depletion also showed reduced export when GANP was depleted. GANP-dependent transcripts were highly expressed, yet short-lived, and were highly enriched in those encoding central components of the gene expression machinery such as RNA synthesis and processing factors. After injection into Xenopus oocyte nuclei, representative GANP-dependent transcripts showed faster nuclear export kinetics than representative transcripts that were not influenced by GANP depletion. We propose that GANP promotes the nuclear export of specific classes of mRNAs that may facilitate rapid changes in gene expression. We used gene expression profiling to compare the abundance of cytoplasmic RNAs after GANP or NXF1 depletion
Project description:Extracellular membrane vesicles (EVs) function as vehicles of intercellular communication in autocrine or paracrine manner. We report that cancer-derived EV biomaterials reach nuclei of human melanoma and breast carcinoma cells and multipotent mesenchymal stromal cells (MSCs) through Rab7+ late endosome subdomains that penetrate into nuclear envelope invaginations. MSCs were exposed to cancer Evs in the presence or absence of drugs that block nucler import or export through the nuclear pores. Depletion of CD9 or inhibition of importin β1, two EV-associated molecules, abrogated the nuclear localization of EV-derived biomaterials and EV-induced early changes in MSC transcriptome notably in genes involved in inflammation. Also inhibition of nuclear export by leptomycin B inhibited early changes in MSC transcriptome. This novel cellular pathway may become a cancer therapeutic target. Overall design: mRNA-Seq Human mesenchymal stromal cells alone or exposed to cancer Evs in the presence or absence of uptake modulators
Project description:Nuclear export of mRNA is essential for eukaryotic cells to establish the flow of genetic information in the nucleus to protein synthesis in the cytoplasm. This transport process is highly regulated to ensure efficient and accurate gene expression. Viruses are well known for their ability to manipulate host gene expression. Here, we report that ORF10 of Kaposi’s sarcoma associated herpesvirus (KSHV), a nuclear DNA virus, inhibits mRNA export in a transcript-selective manner to control cellular gene expression. This export inhibitory effect of ORF10 requires the interaction with an RNA export factor, Rae1. Genome-wide analysis by RNA sequencing revealed the subset of cellular mRNAs whose nuclear export is blocked by ORF10. The 3’ untranslated regions (3’ UTRs) of ORF10-targeted transcripts confer their sensitivity to nuclear export inhibition by ORF10. In the context of KSHV replication, the interaction of ORF10 with Rae1 is important for the virus to express viral genes and produce infectious virions. Our results suggest that a nuclear replicating DNA virus can selectively interfere with RNA export through Rae1 to restrict host gene expression for optimal viral replication. Overall design: 1. Study lytic replication profile of KSHV WT and KSHV ORF10 mutant. 2. Study role of ORF10 on host mRNA nuclear export
Project description:Eukaryotic mRNAs undergo a cycle of transcription, nuclear export, and degradation. A major challenge is to obtain a global, quantitative view of these processes. Here we measured the genome-wide nucleocytoplasmic dynamics of mRNA in Drosophila cells by metabolic labeling in combination with cellular fractionation. By mathematical modeling of these data we determined rates of transcription, export and cytoplasmic decay for >5,000 genes. We characterized these kinetic rates and investigated links with mRNA features, RNA-binding proteins (RBPs) and chromatin states. We found prominent correlations between mRNA decay rate and transcript size, while nuclear export rates are linked to the size of the 3'UTR. Transcription, export and decay rates are each associated with distinct spectra of RBPs. Specific classes of genes, such as those encoding cytoplasmic ribosomal proteins, exhibit characteristic combinations of rate constants, suggesting modular control. Overall, transcription and decay rates have a major impact on transcript abundance, while nuclear export is of minor importance. Finally, correlations between rate constants suggest global coordination between the three processes. Our approach should be generally applicable to other cell systems and provides insights into the genome-wide nucleocytoplasmic kinetics of mRNA. Overall design: 24 RNA-seq experiments comprising 2 biological replicates: pre-exsiting nuclear mRNA time 0h (samples 1&13), pre-exsiting nuclear mRNA time 0.5h (samples 2&14), pre-exsiting nuclear mRNA time 1.5h (samples 3&15) , pre-exsiting nuclear mRNA time 3h (samples 4&16), pre-exsiting nuclear mRNA time 5h (samples 5&17), pre-exsiting nuclear mRNA time 7.5h (samples 6&18), pre-exsiting cytoplasmic mRNA time 0h (samples 7&19), pre-exsiting cytoplasmic mRNA time 0.5h (samples 8&20), pre-exsiting cytoplasmic mRNA time 1.5h (samples 9&21) , pre-exsiting cytoplasmic mRNA time 3h (samples 10&22), pre-exsiting cytoplasmic mRNA time 5h (samples 11&23), pre-exsiting cytoplasmic mRNA time 7.5h (samples 12&24)
Project description:The essential adaptation of X-linked gene expression to the X chromosome copy number variation (called dosage compensation, DC) has been widely studied as a model of chromosome-wide gene regulation. In C. elegans, DC is achieved by two fold downregulation of gene expression from both X copies in hermaphrodites. The dosage compensation complex (DCC), a multiprotein complex structurally similar to mitotic condensins, restricts RNA polymerase progression. Higher order chromatin structures have therefore long been suggested to regulate X-linked gene expression. Here we show that in C. elegans males, the single X chromosome interacts broadly with nuclear pores, while in hermaphrodites the DCC impairs this interaction. Using microscopic measurements we find that the X chromosome is located at the nuclear periphery in males and internal in hermaphrodites, while compaction was higher for the X chromosome than for autosomes but surprisingly comparable between sexes. Mechanistically, we show that a single motif enriched on X, sufficient for DCC loading in hermaphrodites, autonomously targets an autosomal locus to the nuclear periphery specifically in males. Using DNA adenine methyltransferase identification (DamID), we demonstrate that the perinuclear interaction domains are nuclear pores. Dynamic polymer modeling shows that this discrete pore anchoring can explain the high compaction of the male X chromosome. Together, our results put forward a structural model of DC, by demonstrating that X-specific sequences mediate interactions with nuclear pores, thereby locating the X chromosome in active perinuclear domains, while the DCC physically moves X-linked genes away from these transcriptionally active neighborhoods. Overall design: Examination of DamID pattern in 3 different strains with at least 2 replicates per strain, in male or hermaphrodite L4 animals
Project description:Nuclear export of mRNA is an essential process for eukaryotic gene expression. TREX complex couples the gene expression from transcription and splicing to mRNA export. Sub2, a core component of TREX complex in yeast is diversified to two closely related RNA helicases, UAP56 and URH49 in human.UAP56 and URH49 are required for bulk poly (A)+ RNA export but their target genes are quite different. In conclusion, UAP56 and URH49 have a different function in vivo despite the highly similarity. Overall design: Cytoplasmic RNA was prepared in HeLa cells transfected with control-, UAP56- and URH49-siRNA and analyzed by gene expression array.
Project description:The piRNA pathway is a conserved small RNA-based immune system that protects animal germ cell genomes from the harmful effects of transposon mobilisation. In Drosophila ovaries, most piRNAs originate from dual-strand clusters, which generate piRNAs from both genomic strands. Dual-strand clusters use non-canonical transcription mechanisms. Although transcribed by RNA polymerase II, cluster transcripts lack splicing signatures and polyA tails. mRNA processing is important for general mRNA export mediated by Nuclear export factor 1. Although UAP56, a component of the transcription and export complex, has been implicated in piRNA precursor export, it remains unknown how dual-strand cluster transcripts are specifically targeted for piRNA biogenesis by export from the nucleus to cytoplasmic processing centers. Here we report that dual-strand cluster transcript export requires CG13741/Bootlegger and the Drosophila Nuclear export factor family protein, Nxf3. Bootlegger is specifically recruited to piRNA clusters and in turn brings Nxf3. We find that Nxf3 specifically binds to piRNA precursors and is essential for their export to piRNA biogenesis sites, a process that is critical for germline transposon silencing. Our data shed light on how dual-strand clusters bypass canonical mRNA features to be specifically exported via Nxf3, ensuring proper piRNA production